To enjoy the advantages gained by wearing contact lenses it is necessary to carry out the time consuming and cumbersome task of cleaning and disinfection the contact lenses. The procedure differs depending on the type of contact lenses in question e.g. hard lenses or soft lenses.
In all cases, the contact lenses need to be cleaned and disinfected periodically, to avoid infection and discomfort for the wearer, in some cases every morning or evening.
When removed from the eyes the lenses must be stored in a preserving solution. Before wearing the lenses again they must be cleaned, disinfected and rinsed.
The cleaning operation is carried out to remove deposits and debris from the surface of the contact lenses. The cleaning effect is often obtained by treatment with enzymes such as proteases, capable of hydrolysing proteinaceous material to smaller water-soluble subunits.
Disinfection of the contact lenses prevents growth of bacteria on the contact lenses which might lead to infection of the eyes and making it impossible to wear contact lenses for a long period of time. Disinfecting agents such as hydrogen peroxide is widely used.
After the cleaning and/or disinfecting procedure the contact lenses need to be rinsed, to make sure that all enzymatic activities and/or disinfecting agent are removed, e.g. by using a physiological saline solution.
When the contact lenses are not worn the lenses need to be stored under sanitary conditions to secure that they are ready in a clean state for the next wear.
Further it is also important to make sure that the lenses are treated with care to secure that e.g. the shape of the contact lenses is maintained, staining of the lenses is prevented, an acceptable oxygen permeability of the lenses is maintained etc.
Soil deposits are found on all groups of contact lenses, but the easiness of removal differs among the groups. Hard contact lenses are easy to clean, due to only small amounts of soil deposited, and ease of removing soil by rubbing. Soft hydrophillic lenses are more prone to adsorption of soil which is difficult to remove. One reason is that hard rubbing and abrasives might damage the lens.
The major important soil deposits on contact lenses are proteins, lipid deposits and Jelly bumps, mucins, pigments and inorganic compounds.
Wedler (J. Biomed. Mater. Res. Vol. 11, p. 525-535, 1977) has identified tear proteins from extracts of contact lenses. Per lens was found 5-10 .mu.g protein, 1.0-1.2 .mu.g carbohydrates, 5-25 .mu.g phospholipids. Cholesterol and glucose were not detected. Albumin, lysozyme, IgG and .alpha..sub.1 -lipoprotein were found in the deposits.
The main component of Jelly bumps deposits are lipids (Bilbaut et al., Exp. Eys. Res., Vol. 43, p. 153-165, 1986). These are often seen on contact lenses with high water content, particularly extended wear contact lenses (Pohlzhofer, Deutsche Optiker Zeitung, Vol. 40, p.40-100, 1985 and Sack et al. Investigative Ophthalmology & Visual Science, Vol. 28, p. 842-849, 1987).
A plethora of methods for removing deposits from contact lenses are known. Contact lenses are often cleaned with enzymes. U.S. Pat. No. 3,910,296 (Allergan) describes a method for cleaning contact lenses by the use of a protease.
U.S. Pat. No. 4,670,178 (Allergan) discloses a method for simultaneous cleaning and disinfection contact lenses with a protease in hydrogen peroxide. The cleaning is effected by protease and shown to be very efficient.
CA 1,146,881 (Bedding) points out a method for cleaning contact lenses using enzymes, where the cleaning procedure is followed by rinsing of the lenses, e.g. with saline, to remove active enzymes from the lens.
EP patent nr. 257.942 (Hoya Corporation) describes a contact lens cleaning kit comprising an oxidising agent and reducing agent in such a form that they do not react with each other in the kit. When placed in the water, at the same time, the major portion of the oxidant dissolves more rapidly than the major portion of the reductant. The lenses can be worn immediately after treatment without the need for water washing.
CA patent application nr. 2,044,072 (Webb), WO 93/17720 (Webb) and EP patent application nr. 196,151 (Hopkinson) disclose chloramine-T used for disinfecting contact lenses. No use of proteases is mentioned in these patent documents.
U.S. Pat. No. 5,057,414 (Stief et al.) concerns determining activity of serine proteases and inhibitors in plasma, including treatment with e.g. chloramine-T or chloramine-B as an oxidizing agent and a detergent to inactivate specific inhibitors. The patent does not concern cleaning or disinfecting of contact lenses.
EP patent application nr. 147,100 (Ciba Geigy) concerns cleaning and disinfecting of contact lenses with a hydrogen peroxide solution in the presences of a solid sustained release composition which slowly releases a peroxide inactivator. The lenses may be treated with a wetting or comfort solution before inserting into the eyes. However, cleaning and disinfection with hydrogen peroxide does not remove proteinaceous deposits effectively from the surface of the contact lenses.
EP patent application nr. 279.401 (Dr. Thilo & Co. Gmbh) discloses a disinfection and cleaning product for contact lenses containing a chlorine releasing compound, at least one protease and conventional formulation assistants. Initially the chlorine releasing compound, which must be characterized as a strong disinfecting agent, is added to the solution. After sufficient disinfecting, the protease is added to clean the lenses by degrading protein deposits on the lenses surface. The remaining chlorine releasing compound is inactivated by the protease. After the disinfecting and cleaning process the contact lenses must be rinsed thoroughly to remove active protease to avoid damage of the eyes.
A drawback of the techniques disclosed in the prior art documents is that the cleaning and disinfecting of contact lenses with enzymes must be succeeded by a thorough rinsing procedure to secure removal of all remaining enzyme activity before inserting the contact lenses into the eyes. This makes the procedures cumbersome and implies a risk of forgetting the rinsing step, which may lead to exposing the eyes to enzymatic activity and/or disinfecting agents, which will irritate or even might damage the eyes.